Rosmarinus (Rosemary)

The botanical name Rosmarinus is derived from old Latin for “dew of the sea,” possibly for its origins in coastal Mediterranean areas. Rosemary was valued by the ancients as a sacred and medicinal plant and continues to have numerous herbal and culinary uses among many cultural groups.

Only One Species

Of the dozens of cultivar forms ranging from groundcovers to tall shrubs, all belong to only one species, Rosmarinus officinalis. All are edible but with somewhat differing flavors. 

• Gardeners are well advised to purchase only those plants with labels specifying height. Unspecified growth habit likely indicates a seed-grown plant whose size is unpredictable.
• Forms are stiffly upright, mounding, or prostrate in habit.
• Upright forms grow 4-5 ft. high by 5-6 ft. across. A number of dwarf cultivars with vertical branching are suitable for sites where more compact form is desired.
• Mounding forms are typically 2-3 ft. often spreading 4-5 ft. wide.
  • Mounding rosemarys are most common and the most versatile.
  • They may be planted as specimens, among perennial beds, trained as topiaries, sheared as hedges, and used as bank covers or free-form groundcovers.
• Prostrate forms stay low—1-1½ ft.—and spreading.
  • These are suitable for planting on a rock wall or terrace where elongating stems are free to cascade down the face.
  • Prostrate forms also constitute an almost-walk-on groundcover on a flat surface.

Many Named Cultivars

Most gardeners select a named cultivar primarily for growth habit and mature size. However, flower color is often an important consideration depending on floral colors of plant partners.

• All rosemarys attract bees and hummingbirds from mid-autumn until spring when butterflies begin to feed.
• Long bloom is among rosemary’s finest attributes; flowering often begins in October and lasts through March. Most cultivars bloom in shades of blue, but a few are pink or white.
• Long, straight branches are favored for use as wands on barbeque grills. Popular selections include 3-4 ft. 'Blue Spires' with sky-blue blossoms and 5-6 ft. 'Tuscan Blue’ that bears violet-blue flowers.
• ‘Collingwood Ingram’ and similar ‘Ken Taylor’ are popular mounding cultivars for their bright blue, nearly violet flowers and curved branches, but neither lends typical flavor for culinary use.
• ‘Prostratus’ reaches 2 ft. high and spreads 6-8 ft. wide, but may become woody with age. It’s blossoms are violet-blue.
• ‘Huntington Carpet’ is a 1½ ft. preferred low-grower with pale blue blossoms.
• Small, tubular blue flowers range from almost sky blue on ‘Blue Spires’ to the deepest azure on 1-3 ft. ‘Santa Barbara.’
• Cultivars known for outstanding culinary flavor include mounding ‘Majorca Pink’ and ‘Irene’ with lavender-blue flowers, ‘Huntington Carpet’ and taller ‘Arp’ and ‘Hill Hardy’ that all bloom in blue.
• Although most rosemary plants are suited for culinary use, personal taste is the final arbiter.

Easy-Care

Rosemary is considered an evergreen subshrub for the woody lower stems that develop over time. Stems should never be cut back hard into thick bare wood, only into thinner branches bearing foliage.

• Shrubs are completely deer resistant.
• Rosemary adapts easily to Sonoma County’s Mediterranean wet-dry climate. It adapts to any soil with no need for fertilizers.
• Sited in full sun or part shade, rosemary never falters in dry, hot summers or cold, wet winters once established after 1-2 years in the ground.
• Newly planted shrubs require ample water to keep the root ball moist.
• In the hottest months, occasional irrigation may be needed for young plants; otherwise, rosemary is drought tolerant.
• None of the many cultivars require deadheading or pruning. Branching can be allowed to develop like a wild plant and reach in all directions with its twisting branches, or it may be pruned to stay more compact.
• Propagate rosemary from cuttings of non-flowering branches in early summer, or layer established low branches.
• Layering is best done during the rainy season by scooping a shallow trench in moist soil, burying the branch, and putting a rock over it to keep it from springing up. There should be enough roots on the new plant in a few months to detach and transplant.
• Rosemary may be grown indoors in a sunny window as a culinary herb.
• Stems may elongate rapidly in indoor light and require frequent snipping or simply be grown as an herbal decoration. Indoors, plants may be short-lived.

September 2023